1. Field of the Invention
The present invention relates to an air suspension device of an air-back type for use in a vehicle seat, which is adjustable in shock absorbing rate according to a weight of an occupant on the seat by means of a compressed-air supply and exhaust control in an air spring of an air back.
2. Description of Prior Art
A suspension device for use in a vehicle seat has been provided for absorbing an impact or a jolting and rolling of an vehicle on a rough road and retaining a seat height (i.e. a buttock point) at a predetermined level according to a weight of an occupant on the seat. In particular, an air suspension device is known, which utilizes an air spring.
A hitherto air suspension device is of such construction that an air spring is interposed between an upper frame and a lower frame, with a linkage such a pair of X-shaped links provided between the upper and lower frames. The air spring is connected with an air supply source (an air compressor) via a directional control valve having an air supply switch pin and air exhaust switch pin, whereby the compressed air is controlled in supply into or exhaust from the air spring. Further, the linkage is provided at its joint portion with a cam which is actuated responsive to the vertical movements of the linkage so as to depress either of the two switch pins of the directional control valve.
According to the foregoing prior art, when the seat is moved upwardly or downwardly, the linkage thereunder is caused to move in the same direction, with the cam being thereby caused to rotate, pressing either of the air supply and air exhaust switch pins, whereby the air is controlled in flow direction via the control valve so as to be supplied into or exhausted from the air spring. Thus, the air spring is adjusted in inner pressure therein to provide an optimum degree of cushiony effect according to the weight of an occupant on the seat, thereby bringing the seat at a neutral position which is set by the suspension device at a standard line, permitting a good view at the front of an automobile, in reference to the eye point and buttocks point of an occupant whose weight is a fixed one for the standard purpose of the neutral position. Hence, normally, when seated by the occupant, the seat is to be lowered and retained at such neutral position, more or less, and when unseated by him or her, the seat is to be raised and retained above the neutral position.
Consequently, the thus-constructed prior art has been found defective in that, since a certain upwardly repercussive cushiony force is exerted to the occupant sitting on the seat, when he or she stands up from the seat, the seat is raised by the upwardly repercussive inner pressure of the air spring, to be followed by the buttocks of the occupant, with the result that the raised level of the seat creates a hindrance against the occupant who is supposed to descend from the seat and automobile; namely, preventing him or her from easily riding over the increased height of the seat to leave therefrom. Furthermore, when the occupant is supposed to get in and sit on the seat, the unseated seat is positioned at a relatively higher level, which also giving a hindrance against the occupant; namely, the occupant needs to lower the seat forcibly with hands at a level in which he or she may sit on the seat easily, or when the occupant sits on the seat, with a poor seating posture, he or she loses a seating posture and tumbles on the seat, due to the sudden lowering of the seat.